The most common causes of ice dams are inadequate roof insulation and ineffective interior air sealing. Believe it or not, you actually want a cold roof surface in winter! When the warm air from your house warms the bottom of your roof surface, the bottom layer of snow melts and runs down the roof surface (as it is supposed to). However, when it reaches the uninsulated eaves or gutter where there is not warm air from your house heating the roof, the water refreezes.

It is not true that ice dams form because of gutters. This house has no gutters, but conditions are ripe for ice dams due to inadequate interior insulation (I should know - this is my house).

Read More about ice dams.